You probably think that is because it would be the best possible outcome for President Obama. No doubt it would be. If Santorum were the Republican nominee for president, the independents disenchanted with Obama would come flocking back; their fear of Santorum’s unyielding brand of social conservatism would far outweigh their reservations about the incumbent president. A Santorum nomination would likely lead to an epic defeat, ranking with Richard Nixon’s 49-to-1 state landslide victory over George McGovern in 1972, or Ronald Reagan’s 49-to-1 state whipping of Walter Mondale 12 years later.

But it’s not the Democrats I’m really concerned with. It’s the Republicans. For more than a decade now, moderate Republicans have been an endangered species, either losing elections or choosing to retire in the face of a hard-line challenger. The latest casualty was Senator Olympia Snowe of Maine, whose dilemma — caught all too often between her moderate beliefs and pressure from the party to vote the “right” way — was described poignantly by Jonathan Weisman in The Times on Thursday.

In the article, Weisman quoted a number of moderate Republicans lamenting the way the Republican Party is now placing a higher priority on social issues like contraception than on pocketbook issues like jobs and the economy. Christine Todd Whitman, the former Republican governor of New Jersey, noted that many Americans, disenchanted by the poisonous state of American politics, have largely opted out, and that “only the most rabid partisans vote.” In other words, the Republican Party has largely been captured by its most extreme flank. Santorum is their standard-bearer.

But that is also where I see a glimmer of hope. During the McGovern-Mondale era, the Democrats were exactly where the Republicans are now: the party had been taken over by its most extreme liberal faction, and it had lost touch with the core concerns of the middle class, just as the Republicans have now. When I spoke to Whitman this week about what the Republican Party needed to do to become a more inclusive, less rigidly dogmatic party, she said, “It’s going to take some kind of shock therapy.” Those terrible losses in 1972 and, especially, in 1984 were the Democrats’ shock therapy. Just eight years after Mondale’s loss, Bill Clinton was elected president.

What happened in the interim? In effect, moderate Democrats wrested the party back from its most liberal wing. Moderates like Richard Gephardt and Charles Robb began meeting weekly to rethink what the party stood for. One of the people involved in those discussions was Al From, who would later go on to create the Democratic Leadership Council, which became the platform for new Democratic ideas — and, for that matter, for Clinton’s presidential run.

“We had become a party that had stopped worrying about people who were working and only focused on people who weren’t working,” From told me. “The party didn’t understand how big a concern crime was. It had stopped talking about opportunity and growth.”

By the end of the decade, the Democratic Party, embodied by Clinton, was embracing what From would later describe in a speech as the modernization of liberalism: “Progressive policies that create opportunity for all, not just an entitled few; mainstream values like work, family, responsibility, and community; and practical, nonbureaucratic solutions to governing.” This retooled, more inclusive philosophy was successful enough that Clinton became the first Democratic president to win re-election since Franklin Roosevelt.

A party’s base cannot, by itself, swing a presidential election. A party has to have broader appeal. “In 2008,” said Whitman, “John McCain got two million more self-identified social conservatives than George Bush in 2004, yet he was soundly defeated. Constantly looking for ways to drum people out of the party is not a long-term, successful strategy.”

One person who was drummed out is Lincoln Chafee, the governor of Rhode Island, a Republican turned independent. “I care about deficits,” he told me, “but, on social issues, I believe that people should have the right to make their own decisions.” As a result, he said, “I realized that there wasn’t any room in the Republican Party for me.”

When I asked him what it would take to change the Republican Party, he had a quick answer: “What it usually takes is a good drubbing at election time.”

If Mitt Romney takes the nomination and then loses to Obama, the extremists who’ve taken over the party will surely say the problem was Romney’s lack of ideological purity. If, however, Santorum is the nominee — and then loses in a landslide — the party will no longer be able to delude itself about where its ideological rigidity has taken it.

An alcoholic doesn’t stop drinking until he hits bottom. The Republican Party won’t change until it hits bottom. Only Santorum offers that possibility.